Signal transmitting device and signal receiving device

ABSTRACT

In a signal transmitter and a signal receiver according to the present invention, a multiplexing part ( 102 ) multiplexes a video signal and a time-base-compressed audio signal on the basis of a multiplexing control signal to transmit the multiplexed signal through a data line ( 106 ) in the signal transmitter, and a demultiplexing part ( 103 ) demultiplexes a video/audio multiplexed signal received through the data line ( 106 ) into the original video signal and audio signal by a demultiplexing control signal in the signal receiver. Further, a horizontal synchronizing signal or vertical synchronizing signal of the video signal is employed as the multiplexing control signal and the demultiplexing control signal, and the audio signal is time-base-compressed at the transmitting end, to multiplex the audio signal in a blank of the video signal, and the multiplexed audio signal is time-base decompressed at the receiving end.  
     According to the so-configured signal transmitter and signal receiver, it is possible to realize a signal transmission system compliant with the DVI standard, in which the audio signal as well as the video signal can be transmitted.

TECHNICAL FIELD

[0001] The present invention relates to a signal transmitter and asignal receiver.

BACKGROUND ART

[0002] A conventional signal transmission system according to DVI(Digital Visual Interface) standard will be described with reference toFIG. 26. FIG. 26 is a diagram illustrating a structure of theconventional transmission system.

[0003] In this figure, numerals 2601 to 2603 denote TMDSencoders/serializers provided at the transmitting end, which TMDS-encodeinputted component signals such as RED, GREEN, and BLUE signals,serialize the encoded signals, and output the same to transmissionlines. Numerals 2604 to 2606 denote TMDS decoders/recoverer provided atthe receiving end, which TMDS-decode the received signals, recover thedecoded signals, and restore the component signals.

[0004] A DE (Data Enable) signal is a signal indicating a period duringwhich the component signal such as RED, GREEN, and BLUE signals exists,and this is a HIGH active signal. For example, the DE signal is LOW in aperiod of a horizontal synchronizing signal or vertical synchronizingsignal of video.

[0005] CTL (Control) signals CTL 0, CTL 1, CTL 2, and CTL 3 are preparedas control signals. However, these signals are not in use in the presentDVI standard. More specifically, the levels of the signals are always 0.

[0006] The so-configured conventional signal transmission system will bedescribed.

[0007] The TMDS encoders/serializers 2601 to 2603 at the transmittingend convert video signals (RGB signals) inputted at 8 bits into signalsof 10 bits, serialize the converted signals, and output them totransmission lines. The object of the 8 bit-to-10 bit conversion is toreduce data changing points and convert the data into a format that issuitable for high-speed transmission. Further, the TMDSencoders/serializers 2601 to 2603 convert the 2 bit-CTL signals into 10bit-CTL signals and transmit the converted CTL signals to thetransmission lines. The DE signals are also encoded, serialized, andtransmitted to the transmission lines.

[0008] The TMDS decoders/recoverers 2604 to 2606 at the receiving enddecode 10-bit serial data received through the transmission lines intothe 8-bit color signals, the DE signals, and the 2 bit CTL signals todecompress the signals.

[0009] However, the DVI standard is a standard for transmitting onlyvideo signals, and the conventional signal transmission system cannottransmit audio signals.

[0010] The present invention is made to solve the above-mentionedproblem and has for its object to provide a signal transmitter and asignal receiver that can realize a signal transmission system accordingto the DVI standard in which audio signals as well as video signals canbe transmitted.

DISCLOSURE OF THE INVENTION

[0011] According to claim 1 of the present invention, there is provideda signal transmitter which is connected to a signal receiver via atransmission line, comprising: a time-base compression means fortime-base-compressing a first signal; a multiplexing control signalgenerator for generating a multiplexing control signal on the basis of asecond signal; a signal multiplexing means for multiplexing thetime-base-compressed first signal, the second signal and a third signal,employing the multiplexing control signal generated by the multiplexingcontrol signal generator, and outputting a multiplexed signal; and asignal transmitting means for transmitting the multiplexed signal andthe multiplexing control signal to the signal receiver.

[0012] Therefore, it is possible to realize a signal transmission systemwhich transmits the first, second and third signals through the sametransmission line.

[0013] According to claim 2 of the present invention, there is provideda signal transmitter which is connected to a signal receiver via atransmission line, comprising: a time-base compression means fortime-base-compressing a first signal; a multiplexing control signalgenerator for generating a multiplexing control signal on the basis of asecond signal; a signal multiplexing means for multiplexing thetime-base-compressed first signal, the second signal and a third signal,employing the multiplexing control signal generated by the multiplexingcontrol signal generator, and outputting a multiplexed signal; and asignal transmitting means for transmitting the multiplexed signal to thesignal receiver.

[0014] Therefore, it is possible to realize a signal transmission systemwhich transmits the first, second and third signals through the sametransmission line, without transmitting the multiplexing control signalto the signal receiver.

[0015] According to claim 3 of the present invention, in the signaltransmitter as defined in claim 1 or 2, the first signal is an audiosignal, the second signal is a horizontal synchronizing signal or avertical synchronizing signal, and the third signal is a video signal.

[0016] Therefore, it is possible to realize a signal transmission systemaccording to DVI standard, which can transmit the audio signal as wellas the video signal.

[0017] According to claim 4 of the present invention, there is provideda signal transmitter according to DVI transmission standard whichtransmits RGB video signals as serial data having: a first mode oftransmitting the RGB video signals as serial data, and a second mode oftransmitting three signals corresponding to a luminance signal, a colordifference signal and an audio signal, and comprising a switching meansfor switching between the first mode and the second mode.

[0018] Therefore, it is possible to realize a signal transmission systemaccording to the DVI standard, which can transmit the audio signal aswell as the video signal.

[0019] According to claim 5 of the present invention, there is provideda signal receiver which is connected to a signal transmitter via atransmission line, comprising: a first receiving means for receiving amultiplexed signal in which a time-base-multiplexed first signal, asecond signal, and a third signal are multiplexed, from the signaltransmitter; a second receiving means for receiving a multiplexingcontrol signal from the signal transmitter; a demultiplexing means fordemultiplexing the multiplexed signal received by the first receivingmeans into the first and second signals, employing the multiplexingcontrol signal received by the second receiving means; and a time-basedecompression means for time-base-decompressing the first signalobtained by the demultiplexing means.

[0020] Therefore, it is possible to realize a signal transmission systemwhich transmits the first, second, and third signals through the sametransmission line.

[0021] According to claim 6 of the present invention, there is provideda signal receiver which is connected to a signal transmitter via atransmission line, comprising: a receiving means for receiving amultiplexed signal in which a time-base-multiplexed first signal, asecond signal and a third signal are multiplexed, from the signaltransmitter; a detection means for detecting the second signal from themultiplexed signal; a multiplexing control signal generating means forgenerating a multiplexing control signal on the basis of the secondsignal detected by the detection means; a demultiplexing means fordemultiplexing the multiplexed signal into the first, second and thirdsignals, employing the multiplexing control signal; and a time-basedecompression means for time-base-decompressing the first signalobtained by the demultiplexing means.

[0022] Therefore, it is possible to realize a signal transmission systemwhich can demultiplex the multiplexed signal and receive the first,second and third signals through the same transmission line, withoutreceiving the multiplexing control signal from the signal transmitter.

[0023] According to claim 7 of the present invention, in the signalreceiver as defined in claim 5 or 6, the first signal is an audiosignal, the second signal is a horizontal synchronizing signal or avertical synchronizing signal, and the third signal is a video signal.

[0024] Therefore, it is possible to realize a signal transmission systemaccording to the DVI standard, which can transmit the audio signal aswell as the video signal.

[0025] According to claim 8 of the present invention, there is provideda signal receiver according to DVI transmission standard which receivesRGB video signals as serial data having: a first mode of receiving theRGB video signals as serial data and a second mode of receiving threesignals corresponding to a luminance signal, a color difference signaland an audio signal, and comprising a switching means for switchingbetween the first mode and the second mode.

[0026] Therefore, it is possible to realize a signal transmission systemaccording to the DVI standard, which can transmit the audio signal aswell as the video signal.

BRIEF DESCRIPTION OF DRAWINGS

[0027]FIG. 1 is a diagram illustrating a structure of a signaltransmission system according to a first embodiment of the presentinvention.

[0028]FIG. 2 is a diagram illustrating a relationship between a videosignal and an audio signal before time-base compression.

[0029]FIG. 3 is a diagram for explaining a horizontal synchronizingsignal and a vertical synchronizing signal.

[0030]FIG. 4 is a diagram illustrating a structure of a time-basecompression part of the signal transmission system according to thefirst embodiment.

[0031]FIG. 5 is a diagram for explaining time-base compression in thesignal transmission system according to the first embodiment.

[0032]FIG. 6 is a diagram illustrating a structure of a multiplexingpart of the signal transmission system according to the firstembodiment.

[0033]FIG. 7 is a diagram illustrating a state of multiplexing of avideo signal and an audio signal in the signal transmission systemaccording to the first embodiment.

[0034]FIG. 8 is a diagram illustrating a structure of a demultiplexingpart of the signal transmission system according to the firstembodiment.

[0035]FIG. 9 is a diagram illustrating a state of demultiplexing intothe video signal and the audio signal in the signal transmission systemaccording to the first embodiment.

[0036]FIG. 10 is a diagram illustrating a structure of a time-basedecompression part of the signal transmission system according to thefirst embodiment.

[0037]FIG. 11 is a diagram for explaining time-base decompression in thesignal transmission system according to the first embodiment.

[0038]FIG. 12 is a diagram illustrating a structure of a signaltransmission system according to a second embodiment.

[0039]FIG. 13 is a diagram illustrating a structure of a time-basecompression part of the signal transmission system according to thesecond embodiment.

[0040]FIG. 14 is a diagram for explaining time-base compression in thesignal transmission system according to the second embodiment.

[0041]FIG. 15 is a diagram illustrating a state of multiplexing of avideo signal and an audio signal in the signal transmission systemaccording to the second embodiment.

[0042]FIG. 16 is a diagram illustrating a structure of a demultiplexingpart of the signal transmission system according to the secondembodiment.

[0043]FIG. 17 is a diagram illustrating a state of demultiplexing intothe video signal and the audio signal in the signal transmission systemaccording to the second embodiment.

[0044]FIG. 18 is a diagram illustrating a structure of a time-basedecompression part of the signal transmission system according to thesecond embodiment.

[0045]FIG. 19 is a diagram for explaining time-base decompression in thesignal transmission system according to the second embodiment.

[0046]FIG. 20 is a diagram illustrating a structure of a signaltransmission system according to a third embodiment.

[0047]FIG. 21 is a diagram illustrating a state of data in the signaltransmission system according to the third embodiment.

[0048]FIG. 22 is a diagram illustrating an audio separation method atthe receiving end in the signal transmission system according to thethird embodiment.

[0049]FIG. 23 is a diagram illustrating a decoding method at thereceiving end in the signal transmission system according to the thirdembodiment.

[0050]FIG. 24 is a diagram illustrating a structure of a signaltransmission system according to a fourth embodiment.

[0051]FIG. 25 is a diagram illustrating a signal image on a transmissionline in the signal transmission system according to the fourthembodiment.

[0052]FIG. 26 is a diagram illustrating a structure of a conventionalsignal transmission system.

BEST MODE TO EXECUTE THE INVENTION

[0053] Hereinafter, embodiments of the present invention will bedescribed with reference to the drawings. The embodiments described hereare only illustrative and the present invention is not restricted tothese embodiments.

[0054] (Embodiment 1)

[0055] Hereinafter, a signal transmission system according to a firstembodiment will be described with reference to FIGS. 1 to 11.

[0056]FIG. 1 is a diagram illustrating a structure of the signaltransmission system according to the first embodiment.

[0057] In FIG. 1, a signal transmitter comprises a time-base compressionpart 101 which compresses an audio signal on a time axis, and amultiplexing part 102 which multiplexes a video signal and a time-basecompressed audio signal employing a multiplexing control signal andoutputs a video/audio multiplexed signal to a data line 106 (which willbe described later).

[0058] A signal receiver comprises a demultiplexing part 103 whichdemultiplexes the video/audio multiplexed signal in which the videosignal and the audio signal are multiplexed, which has been receivedthrough the data line 106, employing the multiplexing control signal, atime-base decompression part 104 which time-base decompresses the audiosignal obtained by the demultiplexing part 103 to restore the originalaudio signal, and an audio clock reproduction part 105 which reproducesan audio clock on the basis of video clocks received from thetransmitting end through a clock line 107.

[0059] The data line 106 is a serial transmission line connecting thesignal transmitter and the signal receiver.

[0060] Here, the multiplexing control signal controls so as to multiplexthe audio signal in a blank period of the video signal such as ahorizontal synchronizing period and a vertical synchronizing period ofthe video signal, and the multiplexing control signal is generated by amultiplexing control signal generator (not shown).

[0061] Next, an operation of the signal transmission system according tothe first embodiment will be described.

[0062] First, a relationship between the video signal and the audiosignal before the time-base compression is schematically shown in FIG.2. Since the video signal generally has a larger amount of data than theaudio signal, several samples of the video signal temporally correspondto approximately one sample of the audio signal. In the signaltransmission system according to the first embodiment, this video audiosignal is temporally compressed and multiplexed into an area where thevideo signal does not exist. More specifically, the time when the videosignal does not exist is, for example, a horizontal synchronizing periodor vertical synchronizing period of the video signal as shown in FIG. 3.In FIG. 3, a hatched section other than an effective screen correspondsto the synchronizing period. In FIG. 3, a SD screen of MP@ML (MainProfile Main Level) of MPEG 2 is taken as an example. The whole screencomprises 858 pixels (horizontal direction)×525 lines (verticaldirection). Of the whole screen, the effective screen comprises 720pixels (horizontal direction)×480 lines (vertical direction), and adifference between the whole screen and the effective screen is asynchronizing period. The audio signal is multiplexed in thissynchronizing period.

[0063] Next, an operation at the transmitting end will be described.

[0064]FIG. 4 is a diagram illustrating a structure of the time-basecompression part 101. The time-base compression part 101 is constitutedmainly by a memory, and converts a rate of an inputted audio signal.More specifically, a sampling clock of the input is an audio clock faand a clock of the output is a video clock fv. Here, fa refers to anaudio sampling clock frequency and fv refers to a video sampling clockfrequency. Further, the multiplexing control signal is employed tocontrol the output of the time-base compression part 101. As thismultiplexing control signal, the horizontal synchronizing signal or thevertical synchronizing signal is employed.

[0065]FIG. 5 is a diagram illustrating a state of time-base compressionby the time-base compression part 101. The audio signal before time-basecompression is inputted at the sampling frequency fa and the audiosignal after the time-base compression is outputted to the multiplexingpart 102 at the sampling frequency fv. The audio signal after thetime-base compression is outputted in a period during which themultiplexing control signal is LOW. In this figure, for simplification,a reduced number of audio sample points which are outputted in a periodduring which the multiplexing control signal is LOW are shown, while theactually outputted audio sample points are far more than these.

[0066]FIG. 6 is a diagram illustrating a structure of the multiplexingpart 102. The multiplexing part 102 multiplexes the video signal and thetime-base-compressed audio signal, and outputs a video/audio multiplexedsignal. Inputs of the video signal and the time-base-compressed audiosignal to the multiplexing part 102 are switched in accordance with themultiplexing control signal. For this multiplexing control signal, thehorizontal synchronizing signal or vertical synchronizing signal of thevideo is employed.

[0067]FIG. 7 illustrates a state of multiplexing of a video signal andan audio signal by the multiplexing part 102. In this figure, upper twolines indicate a video signal and an audio signal after time-basecompression. A white circle indicates a sampling point of the videosignal and a black circle indicates a sampling point of the audiosignal. The lowest line indicates a state where the audio signal ismultiplexed onto the video signal in a period during which themultiplexing control signal is LOW. This video/audio multiplexed signalis a signal for a transmission line, and is outputted to thetransmission line.

[0068] Next, an operation at the receiving end will be described.

[0069]FIG. 8 is a diagram illustrating a structure of the demultiplexingpart 103. The demultiplexing part 103 demultiplexes the video/audiomultiplexed signal that has been transmitted through the data line 106into a video signal and a time-base compressed audio signal. While ademultiplexing control signal is employed for the demultiplexing, themultiplexing control signal which is supplied from the transmitting endthrough a transmission line provided apart from the data line 106 isemployed as this demultiplexing control signal.

[0070]FIG. 9 is a diagram illustrating a state of the demultiplexing ofthe video signal and the audio signal by the demultiplexing part 103.The video/audio multiplexed signal transmitted through the data line 106is demultiplexed into a video signal and an audio signal in accordancewith the demultiplexing control signal. More specifically, a signalduring a period in which the demultiplexing control signal is LOW istaken as the time-base-compressed audio signal, and a selector of thedemultiplexing part 103 shown in FIG. 8 is set toward the side of theaudio signal output.

[0071]FIG. 10 is a diagram illustrating a structure of the time-basedecompression part 104. The time-base decompression part 104 isconstituted mainly by a memory, and it receives the time-base-compressedaudio signal at the video sampling clock fv in a period during which thedemultiplexing control signal is LOW and outputs the audio signal at theaudio sampling clock frequency fa. Thereby, an audio signal which hasbeen time-base-decompressed as before can be obtained.

[0072]FIG. 11 is a diagram illustrating a state of time-basedecompression by the time decompression part 104. Data during a periodin which the demultiplexing control signal is LOW is taken as an audiosignal, and the time-base-compressed audio signal is inputted at thesampling frequency fv only for the period in which the demultiplexingcontrol signal is LOW and this signal is outputted at the samplingfrequency fa, thereby obtaining the time-base-decompressed audio signal.

[0073] Next, an operation of the audio clock reproduction part 105 willbe described., At the receiving end, on the basis of the video clockthat has been transmitted from the transmitting end, a PLL (Phase LockLoop) control is performed to reproduce the audio clock, and the audioclock is supplied to the time-base decompression part 104.

[0074] As described above, in the signal transmission system accordingto the first embodiment of the present invention, the multiplexing part102 at the transmitting end multiplexes the video signal and thetime-base compressed audio signal on the basis of the multiplexingcontrol signal, whereby the video signal and the audio signal can betransmitted through the same data line 106. Further, at the receivingend, the video/audio multiplexed signal which has been received throughthe data line 106 can be demultiplexed into the video signal and theaudio signal in accordance with the demultiplexing control signal.

[0075] Further, the horizontal synchronizing period or verticalsynchronizing period of the video signal is employed as the multiplexingcontrol signal and the demultiplexing control signal, and the audiosignal is time-base-compressed at the transmitting end andtime-base-decompressed at the receiving end, whereby the audio signalcan be multiplexed in blanks of the video signal and separatedtherefrom.

[0076] (Embodiment 2)

[0077] Hereinafter, a signal transmission system according to a secondembodiment will be described with reference to FIGS. 12 to 19.

[0078]FIG. 12 is a diagram illustrating a structure of the signaltransmission system according to the second embodiment.

[0079] In FIG. 12, a signal transmitter comprises a time-basecompression part 201 which time-base-compresses an audio signal, amultiplexing part 202 which multiplexes a video signal and the audiosignal employing a multiplexing control signal and outputs a video/audiomultiplexed signal, and a multiplexing control signal processing part208 which processes the multiplexing control signal.

[0080] A signal receiver comprises a demultiplexing part 203 whichdemultiplexes the video/audio multiplexed signal received through a dataline 206, a time-base decompression part 204 whichtime-base-decompresses the audio signal obtained by the demultiplexingpart 203, and an audio clock reproduction part 205 which reproduces anaudio clock from a video clock received from the transmitting endthrough a clock line 207.

[0081] The data line 206 is a transmission line connecting the signaltransmitter and the signal receiver.

[0082] The signal transmission system according to the second embodimentdiffers from the signal transmission system of the first embodiment inthat the multiplexing control signal is not given to the receiving endin the signal transmission system according to the second embodiment.

[0083] Hereinafter, an operation of the signal transmission systemaccording to the second embodiment will be described. The time-basecompression part 201 time-base-compresses the audio signal like in thefirst embodiment, while the multiplexing control signal for thetime-base compression is different from that in the first embodiment.

[0084]FIG. 13 is a diagram illustrating a structure of the time-basecompression part 201. The time-base compression part 201 is constitutedby a memory like the time-base compression part 101 of the firstembodiment, and converts a sampling rate of the audio signal. In thefirst embodiment, as the control signal for this memory, themultiplexing control signal, i.e., the horizontal synchronizing signalor the vertical synchronizing signal is used as it is, while in thissecond embodiment this multiplexing control signal is somewhat processedto be employed. More specifically, a signal which falls after counting avideo sampling clock during an L-clock period (L×1/fv sec.) sincefalling of the multiplexing control signal (horizontal synchronizingsignal or vertical synchronizing signal) is employed. The object of thisprocessing is to provide a no-signal period (L-clock period) before theaudio signal after the time-base compression, and make this no-signalperiod recognized at the receiving end as a switching timing between thevideo signal and the audio signal.

[0085]FIG. 14 is a diagram illustrating a state of time-base compressionby the time compression part 201. In this figure, the relationshipbetween the audio signal before the time-base compression and the audiosignal after the time-base compression is almost the same as that in thefirst embodiment, while the audio signal after the-time-base compressionis delayed from the falling of the multiplexing control signal by Lclocks. This L-clock period is in a no-signal state.

[0086]FIG. 15 is a diagram illustrating a state of multiplexing of thevideo signal and the audio signal in the second embodiment. As shown inFIG. 14, an L-clock no-signal period is provided between the videosignal and the time-base-compressed audio signal. In this secondembodiment, samples of the time-base-compressed audio signal that is tobe multiplexed with the video signal are defined as a video samplingclock of a M-clock period (M×1/fv sec.). These L and M are integershaving fixed values. The multiplexing control signal processing part 208generates a new multiplexing control signal which is obtained bydelaying the fall of the multiplexing control signal (horizontalsynchronizing period or vertical synchronizing period) by L clocks.Accordingly, the positions and the number of sampling points of theaudio signal can be recognized at the receiving end, thereby separatingthe audio signal.

[0087]FIG. 16 is a diagram illustrating a structure of thedemultiplexing part 203. In this figure, numeral 210 denotes a selectorcircuit which demultiplexes the multiplexed signal into the video signaland the time-base-compressed audio signal. Numeral 211 denotes aselector control signal generation part which generates a signal forcontrolling the selector circuit 210. Numeral 212 denotes a no-signaldetection part which detects a no-signal state of the video/audiomultiplexed signal transmitted through the transmission line. A counter213 counts a period during which samples of the audio signal exist,i.e., an M-clock period (M×1/fv sec.).

[0088] Next, a specific operation of the demultiplexing part 203 will bedescribed. When detecting a no-signal state of the L-clock period(L×1/fv sec.), the no-signal detection part 212 changes its output levelfrom HIGH to LOW. A timing of the start of counting by the counter 213(falling of the output) is the same as a timing of the falling of theoutput from the no-signal detection part 212. When counting the M-clockperiod since the fall of the output from the no-signal detection part212, the counter 213 raises its output from LOW to HIGH. The selectorcontrol signal generation part 211 is a circuit for calculating an OR(logical add) of the output from the no-signal detection part 212 andthe output from the counter 213. The selector circuit 210 selects A toextract the video signal in a period during which the output from theselector control signal generation part 211 is HIGH, while selecting Bto extract the time-base-compressed audio signal in a period duringwhich the output from the selector control signal generation part 211 isLOW.

[0089]FIG. 17 illustrates a state of demultiplexing of the video signaland the audio signal in the second embodiment. In the video/audiomultiplexed signal on the transmission line, the no-signal periodcontinues for the L-clock period, and thereafter the audio signalsamples exist for the M-clock period. As shown in FIG. 16, the selectoris switched to select B in the period during which the selector controlsignal is LOW and set at A in other cases, whereby the video signal andthe audio signal can be separated and extracted from the video/audiomultiplexed signal.

[0090]FIG. 18 is a diagram illustrating a structure of the time-basedecompression part 204. The time-base decompression part 204 isconstituted by a memory, like the time-base decompression part 104 inthe first embodiment, while the selector control signal shown in FIG. 16is employed as the demultiplexing control signal.

[0091]FIG. 19 is a diagram illustrating a state of time-basedecompression by the time-base decompression part 204. Thetime-base-compressed audio signal is inputted to the time-basedecompression part 204 at the sampling frequency fv only in a periodduring which the demultiplexing control signal, that is, the selectorcontrol signal is LOW, and the inputted signal is outputted at the audiosampling clock fa, thereby obtaining the time-base-decompressed audiosignal.

[0092] As described above, the signal transmission system according tothe second embodiment can realize the same effect as that of the signaltransmission system according to the first embodiment, withouttransmitting the multiplexing control signal to the receiving end. Thatis, in this second embodiment, the signal state in the L-clock period isprovided between the video signal and the audio signal in the periodduring which the video signal and the audio signal are multiplexed, andthe sample points of the audio signal are kept constant as the M-clockperiod, and the receiving end detects the no-signal period of theL-clock period and thereafter takes the M-clock period as a timing ofseparating the audio signal. Accordingly, the audio signal and the videosignal can be separated, without transmitting the multiplexing controlsignal to the receiving end.

[0093] (Embodiment 3)

[0094] Hereinafter, a signal transmission system according to a thirdembodiment will be described with reference to FIGS. 20 to 23. In thethird embodiment, the signal transmission system according to the firstor second embodiment is applied to the DVI (Digital Visual Interface)standard.

[0095]FIG. 20 is a diagram illustrating a structure of the signaltransmission system according to the third embodiment.

[0096] In FIG. 20, numeral 301 denotes a time-base compression part,which is the same as that employed in the first or second embodiment.Numeral 302 denotes a demultiplexing part, which demultiplexes atime-base-compressed audio signal into signals CTL 2, CTL 3 and CTL 1according to the DVI standard, to be superimposed. Numerals 303 to 305denote TMDS encoders/serializers and numerals 306 to 308 denote TMDSdecoders/recoveres, which are the same as those in the prior art.Numeral 309 denotes a composition part which composes the audio signalsobtained from the signals CTL 1, 2, and 3. Numeral 310 denotes atime-base decompression part which decompresses the time-base-compressedaudio signal that is outputted from the composition part 309. In thisfigure, serial data of time-division-multiplexed BLUE and HSYNC or VSYNC(horizontal synchronizing period or vertical synchronizing period) of avideo signal are transmitted through channel 0 of a transmission line,serial data of time-division-multiplexed GREEN and audio (CTL 1) istransmitted through channel 1, and serial data oftime-division-multiplexed RED and audio (CTL 2, 3) is transmittedthrough channel 2.

[0097] An operation of the so-configured signal transmission system willbe described.

[0098]FIG. 21 illustrates states of signals on the transmission linesaccording to the third embodiment.

[0099] First, input data to the TMDS encoders are shown on the top. CTLs(Control Signals) are inserted when a DE (data enable) signal is LOW,and the time-base-compressed audio signals are superimposed on theseCTLs 1, 2 and 3, thereby TMDS-encoding the signals. As signals on thetransmission lines, the encoded CTLs 2 and 3 are superposed in channel2, and the encoded CTL 1 is superposed in channel 1. Thus, on thetransmission line, audio (audio signal) is superposed in the period ofthe horizontal synchronizing signal or the vertical synchronizingsignal. Data which are TMDS-decoded and recovered at the receiving endare shown at the bottom. These recovered data are identical to the inputdata at the transmitting end.

[0100] Next, a method for separating audio at the receiving end will bedescribed.

[0101] As shown in FIG. 22, a prescribed period of the data in channel 0is initially detected by a data prescribed period detection circuit 350.This prescribed period of the data is a horizontal synchronizing periodor a vertical synchronizing period. This prescribed period of the datais detected to generate a DE (Data Enable) signal, a period during whichthe DE signal is LOW is taken as a period during which the audio signalis multiplexed, the DE signal is supplied to the decoding andvideo/audio demultiplexing circuits 351 and 352 for channels 1 and 2,and the video signal and the audio signal are separated by channel 1 and2 decoders. Then, the audio signals of the separated lines (CTL 1, CTL2, and CTL 3) are obtained.

[0102] Next, a decoding method at the receiving end will be described.

[0103] In FIG. 23, the video/audio multiplexed signal that has beentransmitted through channel 2 is subjected to serial/parallel conversionby a serial/parallel conversion circuit 360, this signal is taken as avideo signal during the period in which the DE (Data Enable) signal isHIGH, and the video signal is subjected to 10 bit/8 bit TMDS decoding bya decoder 362, thereby obtaining a RED signal. On the other hand, thissignal is taken as an audio signal during the period in which the DE(Data Enable) signal is LOW, and the audio signal is subjected to 10bit/2 bit TMDS decoding by a decoder 363, thereby obtaining audiosignals in the lines of CTL 2 and CTL 3. Similarly in channel 1, thetransmitted video/audio multiplexed signal is subjected toserial/parallel conversion by a serial/parallel conversion circuit 361,this signal is taken as a GREEN video signal during the period in whichthe DE (Data Enable) signal is HIGH, and the video signal is subjectedto 10 bit/8 bit TMDS decoding by a decoder 364. On the other hand,during the period in which the DE (Data Enable) signal is LOW, thissignal is subjected to 10 bit/2 bit TMDS decoding by a decoder 365,thereby obtaining the audio signal for the CTL 1.

[0104] In this way, the audio signals which are obtained on the CTL(Control) lines are composed by the composition part 309 and furthersubjected to rate conversion by the time-base decompression part 310,thereby obtaining the original audio signal.

[0105] Next, operations of the demultiplexing part 302 and thecomposition part 309 will be described.

[0106] In the demultiplexing part 302, the time-base-compressed audiosignal is demultiplexed into the three lines of CTL 2, 3 and 1, whileonly a line of CTL 2 or two lines of CTL 2 and 3 may be used dependingon the band of the audio signal. In addition, the audio signal may beseparated in the order of CTL 2, 3, 1, 2, 3 and 1, according to theorder of sampling points of the audio signal. In the composition part309, the decoded audio signals transmitted through the transmissionlines are considered that the audio signals are transmitted in the orderof CTL 2, 3 and 1, thereby to compose the audio signals. These threelines can be used not only in this order of CTL 2, 3 and 1 but also inan arbitrary order, while the order of demultiplexing and compositionshould be decided at the transmitting end and the receiving end.

[0107] As described above, in the signal transmission system accordingto the third embodiment, the structure of the signal transmission systemaccording to the first or second embodiment is applied for the DVIstandard. The time-base-compressed audio signal is demultiplexed intothe lines of CTL 2, 3 and 1, and at the receiving end, the audio signalstransmitted by the CTL 2, 3, and 1 are composed to betime-base-decompressed so as to restore the audio signal. Thus, theaudio signal can be also transmitted by a signal transmission systemaccording to the DVI standard which can conventionally transmit onlyvideo.

[0108] (Embodiment 4)

[0109] Hereinafter, a signal transmission system according to a fourthembodiment will be described with reference to FIGS. 24 and 25. Thefourth embodiment differs from any of the first to third embodiments. Inthis fourth embodiment, an audio signal is not transmitted by employingblanks in a video signal like in the first to third embodiments, but oneof three transmission lines that are employed in a signal transmissionsystem of the DVI standard is reserved as a transmission line for audiosignal. That is, in the case of the DVI standard, transmission of thevideo signal is performed for component signals such as RED, GREEN andBLUE, while in the fourth embodiment, a mode in which transmission isperformed with Y-color difference signals such as Y, Pb and Pr is added,and then an unused channel is allocated for the audio signal.

[0110]FIG. 24 is a diagram illustrating a structure of the signaltransmission system according to the fourth embodiment.

[0111] In this figure, numeral 401 denotes a selector, which selects aRED signal or a luminance signal (Y), and supplies the selected signalto a TMDS encoder. Numeral 402 also denotes a selector, which selects aGREEN signal or a Pb/Pr signal. Numeral 403 denotes a selector, whichselects one of a BLUE signal and an audio signal. Numerals 404 to 406denote TMDS encoders/serializers and numerals 407 to 409 denote TMDSdecoders/recoveres. These constituents are identical to those of thefirst to third embodiments.

[0112] The characteristic of this fourth embodiment is the use of Ycolor-difference transmission for transmitting video signals. As the Ycolor-difference transmission, there is for example 4:2:0 transmission.The 4:2:0 transmission is one in which the color signal rate is a halfof the luminance signal rate, as shown in FIG. 25. More specifically,the number of samples of the color signal is a half of the number ofsamples of the luminance signal. Thereby, the video signal can betransmitted on two channels through the transmission lines of the DVI.More specifically, the luminance signal is transmitted on channel 2, andthe color signal Pb/Pr is transmitted on channel 1. The audio signal issuperimposed in unused channel 0. This audio signal is the originalaudio signal which is not time-base-compressed.

[0113] As described above, the signal transmission system according tothe fourth embodiment further has the mode in which the transmission isperformed with the Y color-difference signals such as Y, Pb and Pr, andan unused channel is allocated to the audio signal, thereby realizing asignal transmission system compliant with the DVI standard, in which theaudio signal as well as the video signal can be transmitted.

[0114] Further, in the fourth embodiment, Y, Pb/Pr, and audio signalsare allocated to channel 2, channel 1, and channel 0, respectively, butthe allocation is not restricted to the above-mentioned manner.

[0115] Further, in the embodiments according to the present invention,multiplexing and transmission of signals are performed by themultiplexing part, but the multiplexing and transmission can beperformed separately by different components.

APPLICABILITY IN INDUSTRY

[0116] A signal transmitter and a signal receiver according to thepresent invention are available as a signal transmission systemcompliant with the DVI standard, which can transmit an audio signal aswell as a video signal.

1. A signal transmitter which is connected to a signal receiver via atransmission line, comprising: a time-base compression means fortime-base-compressing a first signal; a multiplexing control signalgenerator for generating a multiplexing control signal on the basis of asecond signal; a signal multiplexing means for multiplexing thetime-base-compressed first signal, the second signal and a third signal,employing the multiplexing control signal generated by the multiplexingcontrol signal generator, and outputting a multiplexed signal; and asignal transmitting means for transmitting the multiplexed signal andthe multiplexing control signal to the signal receiver.
 2. A signaltransmitter which is connected to a signal receiver via a transmissionline, comprising: a time-base compression means fortime-base-compressing a first signal; a multiplexing control signalgenerator for generating a multiplexing control signal on the basis of asecond signal; a signal multiplexing means for multiplexing thetime-base-compressed first signal, the second signal and a third signal,employing the multiplexing control signal generated by the multiplexingcontrol signal generator, and outputting a multiplexed signal; and asignal transmitting means for transmitting the multiplexed signal to thesignal receiver.
 3. The signal transmitter as defined in claim 1 or 2,wherein the first signal is an audio signal, the second signal is ahorizontal synchronizing signal or a vertical synchronizing signal, andthe third signal is a video signal.
 4. A signal transmitter according toDVI transmission standard which transmits RGB video signals as serialdata having: a first mode of transmitting the RGB video signals asserial data, and a second mode of transmitting three signalscorresponding to a luminance signal, a color difference signal and anaudio signal, the signal transmitter comprising a switching means forswitching between the first mode and the second mode.
 5. A signalreceiver which is connected to a signal transmitter via a transmissionline, comprising: a first receiving means for receiving a multiplexedsignal in which a time-base-multiplexed first signal, a second signal,and a third signal are multiplexed, from the signal transmitter; asecond receiving means for receiving a multiplexing control signal fromthe signal transmitter; a demultiplexing means for demultiplexing themultiplexed signal received by the first receiving means into the firstand second signals, employing the multiplexing control signal receivedby the second receiving means; and a time-base decompression means fortime-base-decompressing the first signal obtained by the demultiplexingmeans.
 6. A signal receiver which is connected to a signal transmittervia a transmission line, comprising: a receiving means for receiving amultiplexed signal in which a time-base-multiplexed first signal, asecond signal and a third signal are multiplexed, from the signaltransmitter; a detection means for detecting the second signal from themultiplexed signal; a multiplexing control signal generating means forgenerating a multiplexing control signal on the basis of the secondsignal detected by the detection means; a demultiplexing means fordemultiplexing the multiplexed signal into the first, second and thirdsignals, employing the multiplexing control signal; and a time-basedecompression means for time-base-decompressing the first signalobtained by the demultiplexing means.
 7. The signal receiver as definedin claim 5 or 6, wherein the first signal is an audio signal, the secondsignal is a horizontal synchronizing signal or a vertical synchronizingsignal, and the third signal is a video signal.
 8. A signal receiveraccording to DVI transmission standard which receives RGB video signalsas serial data having: a first mode of receiving the RGB video signalsas serial data and a second mode of receiving three signalscorresponding to a luminance signal, a color difference signal and anaudio signal, the signal receiver comprising a switching means forswitching between the first mode and the second mode.